Piperonal as antifoggant and stabilizer

ABSTRACT

A LIGHT-SENSITIVE SILVER HALIDE EMULSION AND THE PHOTOGRAPHIC MATERIAL PREPARED THEREFROM, BOTH OF WHICH CONTAIN AS AN ANTIFOGGANT AND STABILIZER A PIPERONAL COMPOUND HAVING THE STRUCTURAL FORMULA:   6-(O=CH-)-1,3-BENZODIOXOLE

United States Patent US. Cl. 96-665 1 Claim ABSTRACT OF THE DISCLOSURE A light-sensitive silver halide emulsion and the photographic material prepared therefrom, both of which contain as an antifoggant and stabilizer a piperonal compound having the structural formula:

CHO

This invention relates in general to photography and in particular to the provision of novel antifogging and stabilizing compounds for use in connection with the preparation and/or processing of photographic silver halide emulsions.

It is well known that light-sensitive materials such as gelatin silver halide emulsion exhibit a marked tendency to fog. The term fog as used in the photographic art connotes that portion of the density obtained upon development which arises by virtue of factors other than the photographic exposure. The fog may be attributable to a number of influences including, for example, excessive ripening of the emulsion, prolonged storage of the film and especially under conditions of elevated temperature and/or humidity, as well as by prolonged development of the exposed emulsion, etc.

Resort to rapid-developing operations which usually require the use of elevated temperatures likewise presents severe problems of fog.

As is well known, it is conventional practice in the photographic art to incorporate into silver halide emulsions various types of sensitizing agents in order to enhance their sensitometric response. For example, gold or sulphur sensitizing agents or combinations of both have been extensively employed for such purposes, Invariably, however, prior attempts to achieve ultimate speed in photographic emulsions so sensitized have been to a large extent vitiated by the concomitant occurrence of fog.

Furthermore, similar fogging problems are encountered when employing sensitizers of the reduction type, such sensitizing agents usually being employed to augment the sensitizing properties of gold, sulphur and the like. As examples of compounds known to function as reduction sensitizers in silver halide emulsions there may be mentioned in particular the following: imino-amino-methanesulfinates; hydrazine and hydrazine derivatives; certain amines such as diethylenetriamine, triethylenetetramine, triethanolamine; silene compounds having a silicon-hydrogen bond; spermine; sodium formaldehyde sulfoxolate; stannous chloride; alkalimetal sulfite; sugars such as lactose, dextrose, ascorbic acid and the like. However, like many of their predecessors, the use of the aforementioned compounds has likewise been encumbered by severe fogging problems and especially when employed in the prep 3,565,623 Patented Feb. 23, 1971 aration of photographic silver halide emulsions of the high speed type.

The foregoing problems have in many instances necessitated resort to the use of antifoggant compounds such as benzotriazole, nitrobenzimidazole, phenylmercaptotetrazole and the like. However, these particular compounds have been ascertained to provide somewhat sub-optimum results since, while serving as effective antifoggants, they display a pronounced tendency to reduce emulsion speed. To a great extent, the depression on emulsion sensitivity has more than offset any possible benefits arising from their use.

Considerable investigation likewise indicates that the gelatin itself may be a source of fogging problems. Quite obviously, the use of gelatins which are not properly balanced with regard to their content of sensitizing, restraining and antifogging substances frustrates attempts to alleviate the fogging problem. Despite the fact that the manufacturers of photographic gelatins are, for the most part, highly skilled in controlling the proper content of sensitizers, antifoggants, etc., e.g., by careful selection and treatment of the raw materials, bones and hides, as well as the careful control of the acid or alkaline treatment of the extraction of gelatin, and selection of filter aids, it is nevertheless frequently experienied that the gelatin material remains a casual factor with regard to fog. While the substantial majority of commercial gelatins have been ascertained to be offensive in this regard, the fogging problem has been found to be highly manifest with pigskin, chicken feet and rabbit skin type gelatins and especially when utilized in the preparation of emulsions of the ammonia type.

Photographic silver halide emulsions are usually provided with one or more speed-increasing agents, e.g., the polyoxylalkylenes and derivatives thereof for purposes of compensating for the depression in sensitometric response caused by the antifoggant. However, the net result has often been a re-establishment of the fogging problem.

The fogging problem is also aggravated by the use of hardening agents for the photographic emulsion, e.g., formaldehyde, glyoxal, etc.

In accordance with the discovery forming the basis of the present invention, it has been found that the antifogging and stabilization characteristics of light-sensitive silver halide emulsions can be synergistically modified to advantage by the utilization of a particular class of chemical compounds in connection with the preparation and/ or processing of such emulsions.

Thus, a primary object of the present invention resides in the provision of improved antifogging and stabilizer compounds in which the foregoing and related disadvantages are eliminated or at least mitigated to a substantial degree.

Another object of the present invention resides in the provision of light-sensitive silver halide emulsions containing a compound which stabilizes the emulsion against fogging while exhibiting little, if any, tendency to reduce the speed or contrast of such emulsions.

A further object of the present invention resides in in the provision of light-sensitive silver halide emulsions and photographic elements prepared therewith containing an antifogging compound which is substantially de void of any tendency to reduce the sensitivity of the emulsion to light of longer wave length due to the presence of one or more sensitizing dyes.

A still further object of the present invention resides the provision of light-sensitive silver halide emulsions posed photographic silver halide emulsion wherein at least one of the steps of pre-treating or developing the emulsion is effected in the presence of a novel stabilizing compound to be more fully described hereinafter.

The attainment of the foregoing and related objects is made possible in accordance with the broader aspects of the present invention by the incorporation in a lightsensitive photographic element of, developing solution and/or pre-treatment solution of a piperonal compound of the following structural formula:

(III-IO O OCH2 It will be understood that the present invention contemplates the use of substituted derivatives of the above depicted compound, i.e., derivatives containing one or more substituents which are substantially inert under the conditions prescribed for their use. The nature of such substituents is not particularly critical with the obvious qualification that the antifogging and stabilizing properties be not deleteriously affected. Such substituents include for example, alkyl, alkoxy, halogen, nitro and the like.

The compounds contemplated for use herein are available commercially and can be synthesized according to preparatory techniques described in the published literature, e.g., Beilstein, vol. 19, p. 115.

Improved fog reduction and other beneficial effects are obtained when the aforementioned compounds are incorporated into the silver halide emulsion as ripening finals or as coating finals. As is well known, ripening finals are added during the ripening or sensitivity increasing stage of the emulsion making process. Such additions may be effected before, during or after the decomposition of the soluble silver salt such as silver nitrate by means of a soluble halide such as potassium bromide, sodium chloride or the like in the presence of a suitable colloid carrier such as gelatin, polyvinyl alcohol, solubilized casein albumen or the like.

Coating finals are added to the emulsion just prior to coating on a suitable support such as glass, paper or film at a time when the emulsion has nearly attained its maximum sensitivity.

It will also be understood that the novel stabilizers of the present invention may be incorporated in a layer adjacent to the sensitized layer such as an anti-abrasion layer. The stabilizing compound may be utilized in concentrations varying over a relatively wide range; for example, when added to the light-sensitive silver halide emulsion layer as a ripening final, it is found that optimum realization of results provided herein are assured with stabilizer concentrations ranging from as low as 25 milligrams up to about 500 milligrams per 1 mole of silver halide. The concentration selected within the aforestated range will depend to a large extent on the type of emulsion employed and thus, it is advisable to determine the optimum concentration from case to case. If added during the emulsion preparation stage, stabilizer concentrations ranging from 2 to 500 milligrams per mole of silver halide are found to be quite reasonable.

The stabilizer compounds contemplated herein can be applied in a variety of ways to impart stability to photographic elements. As previously mentioned, they may be included as a constituent of the emulsion layer, of a surface layer over the emulsion or alternatively, over the base or support.

Further embodiments of the present invention contemplate the addition of such compounds to at least one of the developing, fixing, washing, drying, etc., solutions utilized in the processing of the exposed emulsion.

In general, it is found that the improvements provided by the present invention are particularly manifest according to procedures whereby development is effected in the presence of said stabilizer compounds. This, of course, would be the case should the stabilizer be included in the light-sensitive photographic element, the developing solution and/or suitable developer pre-bath. In any event, when incorporated into the photographic developer or other processing bath, the stabilizers of the present invention are preferably employed in concentrations ranging from about 10 to about 500 milligrams per liter of solution, with a range of about 20 milligrams to about 200 milligrams per liter being particularly preferred.

In addition to being useful in orthochromatic and panchromatic emulsions, the stabilizers may also be used in nonsensitized emulsions, X-ray emulsions, paper emulsions, color emulsions and the like. If used with sensitizing dyes, they may be added to the emulsion before or after dye addition. Moreover, the present stabilizers may also be employed in conjunction with other known antifoggants and stabilizers, reduction or sulfur sensitizers, metal and noble metal sensitizers or in combination with with other additive agents and the like.

The stabilizer may also be employed in gelatin or other water-permeable colloids including polyamides or a mixture of gelatin with a polyamide as described in US. Pat. No. 2,289,775; polyvinyl alcohol and gelling compound as described in US. Pat. No. 2,249,537; polyvinyl acetaldehyde acetal resins and partially hydrolyzed acetate resins described in US. Pats. Nos. 1,939,422 and 2,036,092; cellulose derivatives, e.g., cellulose nitrate, cellulose acetate, and the lower fatty acid esters of cellulose including sample and mixed esters and ethers of cellulose and the like.

When preparing the photographic emulsion in accordance with the present invention, a solution of the stabilizer in a suitable solvent, such as water, alcohol, dimethyl formamide, N-methyl-Z-pyrrolidone, or alcohol-water mixture adjusted to a neutral or slightly alkaline pH, i.e., about 6 to 8 is made up and the solution mixed with the emulsion at any convenient stage during its preparation, but preferably during ripening or just prior to coating.

The following examples are given for purposes of illustrating the present invention in greater detail, and are not to be considered in any way as being limitative thereof.

EXAMPLE I A high speed negative ammonia emulsion was prepared using the formula described on p. 332, Photographic Chemistry, vol. 1, by Pierre Glafkides (1958). A pigskin gelatin was used. This emulsion was called (a). A second emulsion (b) was prepared which differed from emulsion (a) in that we used, in the second ripening (after washing) 1 cc. of a 5% solution of piperonal in N-methyl-2- pyrrolidone.

These emulsions were then readied for coating on film base, that is, melted at 40 C., necessary coating finals were added, such as stabilizers and hardeners. Emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type 1B Sensitometer and developed in a de- Water to make 1 liter.

The sensitometric results were as follows:

Emulsion Relative speed Fog 12 (lov.

EXAMPLE II Example II differs from Example I in that the pigskin gelatin was replaced With an inert bone gelatin. There was added to the second ripening (after washing) a gold thiocyanate solution, which was prepared according to Glafkides (see Example I), p. 319. There was also added a solution 1: 10,000 of Na S O as a sulfur sensitizer (Glafkides, p. 284) and a solution of hydrazine as a reduction sensitizer. The pH and pAg was adjusted by adding dilute sulfuric acid and KBr solution. Since the optimum amounts of these solutions depend on the selection of the gelatin, they have to be determined from case to case by fractional experiments (see Statistical Methods for Chemists by W. J. Youden, 1951, pp. l061l5). The so-called emulsion is called (a). Emulsion (b) differed from emulsion (a) in that We used 2 cc. of a solution of piperonal in the after ripening per 1 kg. emulsion. The re sults were as follows:

Relative speed Fog 12dev.

Emulsion EXAMPLE III EXAMPLE IV Example II is repeated; however, emulsion sample (a) was prepared utilizing thioacetamide in lieu of Results similar to those described above are obtained when the piperonal compound is replaced in equivalent 6 amounts within the range specified with one or more of the substituted derivatives more explicitly defined hereinbefore.

The present invention has been disclosed with respect to certain preferred embodiments thereof, and there will become obvious to persons skilled in the art various modi fications, equivalents or variations thereof which are intended to be included within the spirit and scope of this invention.

What is claimed is:

1. A process of treating an exposed silver halide emulsion which comprises developing said emulsion in a photographic developing solution containing as an antifoggant and stabilizer from 10 to 500 milligrams per liter of the developing solution of a compound of the following structural formula:

CHO

References Cited C. Absts., vol. 49, 10774i. Chem. Absts., vol. 53, 107c.

NORMAN G. TORCHIN, Primary Examiner M. F. KELLEY, Assistant Examiner US. Cl. X.R. 96-95, 109 

